A few opinions on capturing from SkyHD with HD PVR and converting to MKV

[Emanef]

I've recently bought a Hauppauge HD PVR for recording from Sky HD with the intention of converting them to smaller files for backup.

There are two main questions I have.

Firstly, when recording from standard Sky channels through the HD box, what is the best setting to use? Presumably standard broadcasts are 576 upscaled to 720p or 1080i (depending on how your box is set up). I'll be using a popcorn Hour to watch them, which upscales anyway, so is there any point in capturing those in any more than 576? Or is it better to capture them at 720p (ie set the Sky box to that) and then either keep the resolution or convert to 576? Seems odd to be having a standard pic upscaled to 720, then converted back to 576!

Secondly, recording movies from the HD channels. If I want to convert to mkv of a reasonable quality (ie better than DVD but not as high as the original broadcast) am I better off with 720p or 1080i? 1080i is higher res, but with the interlacing cause problems? Presumably x264 will deinterlace it, so I'm wondering if I'm just better of using 720p?

I know it's an ongoing debate and opinions will always differ, but on the 720p or 1080i issue.... I'm not sure if I can actually see any difference! Not on my 42" screen. Maybe more noticable on a 50"+, but there's certainly not the difference there is between standard and HD!

[Emanef]

Not had a response, but thought I'd bounce this back up...!

I've been trying RipBot as Staxrip won't play with 1080 files. If I convert a 720p with, say 3000 bit rate and a 1080i with the same, which is likely to play back best? I'm trying to work out whether lower res progressive or higher res but interlaced gives the better quality/size compromise. Any opinions?

[poisondeathray]

re-encoding to a goal of 3000kbps, from an HDTV source, you should go with 720p, which means you have to deinterlace before you re-encode. 1080i @ 3000kbps will not look very good - you can verify this for yourself on a short sample

[Emanef]

Why would a 720p capture (ie with the Sky HD box set to output 720p) need de-interlacing? Wouldn't already be prog?

[poisondeathray]

Yep if you captured in 720p you are fine

If you take the 1080i => 720p you would need to deinterlace and re-encode

[Emanef]

Ah, sorry, I've probably not explained properly then. I can capture at both 720p and 1080i, so I'm trying to work out whether it's better to capture at 720p and re-encode to a lower bit rate 720p, or capture at 1080i and recode to a lower bit rate 1080i?

[poisondeathray]

What are you going to do with the original capture? discard it? If so, then just capture at the lower bitrate, you would save a lot of time re-encoding/processing/deinterlacing . If you are saving the original, As a general rule, you want to capture at the highest resolution, highest bitrate.

There are too many variables to answer your question specifically, it depends on many factors e.g. source quality, bitrate, filtering, encoding settings etc...

How are you going to watch this? Interlaced content doesn't look so good on the PC, even when deinterlaced on the fly. You have to use a high quality deinterlacer (takes even longer) or even bob it to look good

[jagabo]

If the Popcorn Hour handles 576i well, and your Sky HD box will output SD sources as 576i, you might as well capture SD as 576i. Capturing upscaled (by the Sky HD box) SD as 720p or 1080i will be a waste of bitrate (bigger frame --> more bitrate). And scaling of interlaced video may create artifacts.

Interlacing will be less of an issue since you are in a PAL area. Most movies will be 720p50 (each film frame displayed twice) or 1080i25 (with both fields from the same film frame). In live sports and news broadcast as 720p50 each frame will be different. When broacast as 1080i it will be fully interlaced. It will be a pain to deal with interlaced video if you're looking at reencode with reduced frame and file size. If the Sky box does an acceptable job of converting 1080i to 720p that would be easiest to deal with.

There are a lot of variables here. I recommend you just experiment and see what works for you.

[Emanef]

I'll be ditching the original recoridngs as they take up too much space, and I'm hoping to get them down to below 2gb on average for the PCH.

The PCH does upscale standard def well, so I'll capture the SD broadcasts at 576, convert to that and let the PCH upscale them on playback.

I've run a few tests. I think I was making a mistake by using high settings on the 1212; I had it set to constant quality of 10mbps with the intention of having a constant high quality file to re-encode at a lower VBR, but it does give hugh files. Setting the 1212 to average bit rate of 8 with a peak of 14 gives considerably smaller files, and 6-14 gives even smaller.

On the tests I did, the captures 1080 files were about 25% larger than the 720 ones (I basically chose a movie, set the Sky HD to play on 30 mins and recorded for 1 min at each setting). On playing back on the PCH, with the PCH set to 1080i output I couldn't see any difference between the 1080 files and the 720 files. Similarly with it set to 720p output, but all were better with the PCH set to 1080i over 720p, so it seems to upscale 720p well as well. I'm going to record a few full movies in this method and try to establish the ideal capture settings for my wants.

One question about the outputted TS/M2TS files. Does converting to x264 give better compression, or are they pretty much the same, just in a different wrapper?

Cheers guys

[jagabo]

If I'm going to reduce the caps to a lower res I capture at the highest bitrate settings to get the best possible source to work with.

[Emanef]

Well that's what my original thoughts were, that capturing at a high constant setting gives a recode a constant high q to play with, but they were mostly 6-8 gig a movie.

I left it recording four movies last night at 720p wiith an average setting of 8, peak 14. I've trimmed them into four indivual files, and they're considerably smaller;
Casino Royale & Zodiac are around 2.5 gb, Predator 2 around 1.8 and Saw 4 around the same. I need to copy them over to the PCH to test them,which I'll do later if I get the chaance.

I'd still rather a little smaller, but I can try some captures with the ave set to 6mbpsto see how they come out.

Is there any point in converting these TS files to MKV/MP4? The PCH plays them all (although only showed details like bit rate, etc whilst playing back with the MKV and MP4, no data shown when playing TS/M2TS), but am I likely to get them any smaller without losing more quality by converting to MKv or MP4? If not, I may as well keep them as TS, although I'm not sure if YAMJ will identify those files (not checked yet!)

[jagabo]

MKV and MP4 have less overhead than TS. Remuxing will reduce the file size by about 5 percent.

Try using Variable (peak) mode to record 720p movies. 24 fps film broadcast as 720p60 have the frames repeated to increase the frame rate. All those repeat frames compress to nearly nothing in VBR mode. The files will be much smaller than when recorded in CBR mode.

[Emanef]

Sky HD is in the UK and they broadcast everything (AFAIK) at 50fps (25 for interlaced). What's the dfference between Variable (Peak) and Variable (Average)?

[jagabo]

Sorry, forget you were in the UK. For 50 fps film is usually sped up to 25 fps and each frame displayed twice. The same VBR rule holds true: all the duplicate frames require very little bitrate so VBR wil be much smaller than CBR at the same quality.

I'm not really sure what the difference is between Hauppauge's Peak and Average methods. After a lot of experiments I was unabled to determine exactly how they differed. In the end I just decided to go with Peak. I don't remember why.

Here are some numbers. I captured the same 1 minute segment from a movie that was recorded on my PVR (NTSC, 1080i30, 720p60). I captured both in CBR and VBR modes with the bitrate sliders at their max settings. The PVR was set up to output 1080i (it was a 1080i recording) and downconverted to 720p.

1080i, vbr peak: 91.6 MB
1080i, vbr average: 92.5 MB
1080i, cbr: 102.6 MB

720p, vbr peak: 55.3
720p, vbr average: 55.6
720p, cbr: 102.8

I haven't examined them very closely, and this particular movie wasn't very sharp, but at first glance I could see no significant difference in quality. So with 720p caps it make sense to use the VBR modes.

[Emanef]

Is there anyway of converting files from TS to MKV without re-encoding? Ie just remuxing to the different wrapper, and keeping the video and audio the same but just losing the wasted overheads?

[jagabo]

Try TsMuxerGUI to extract as elementary streams, then MkvMerge to merge them into MKV.

[Emanef]

Thanks Jagabo. Strangely enough, the two I tried to demux and remux to mkv actually came out slightly bigger than the orginal TS files! Plus they reported as 25fps in Mediainfo (compared to the 50 of the orginal capture)!

You've also answered something I didn't ask but was wondering...... I was trying to work out why 1080 files were larger than 720 files, as I was thinking that, although the 720 are clearly small resolution, I was thinking they were 50 individual frames, but it makes sense that half of them are pretty much duplicated, so take up much less data.

I think I'm going to struggle to get an average movie down to much below 2gb. Am I expecting too much? The only way to get a 100 min movie down to around 1500mb is to have the ave bit rate at about 2000. I'm finding that a 1212 capture with an average of 6 or 7 (which seems to give an actual ave of around 3) is alkmost double that size, but the nearest to keeping a high quality with a smaller file?

[jagabo]

they reported as 25fps in Mediainfo (compared to the 50 of the orginal capture)!

You have to manually specify the frame rate before saving the MKV. It's in the stream specific options for the video stream.

I think I'm going to struggle to get an average movie down to much below 2gb. Am I expecting too much? The only way to get a 100 min movie down to around 1500mb is to have the ave bit rate at about 2000. I'm finding that a 1212 capture with an average of 6 or 7 (which seems to give an actual ave of around 3) is alkmost double that size, but the nearest to keeping a high quality with a smaller file?

You will have to reencode with a smaller frame size if you want to go that small. You're getting down to SD resolution/bitrates.

[Emanef]

Ah, ok. I guess I was thinking that 720 would be around 30% larger than DVD res 576, but I obviously misunderstood the logic behind it! So is around 3000bps around the minimum ave bit rate I'll be needing for a decent 720?

I'll try the remuxing again I did it pretty quickly anyway.

[jagabo]

1280x720 is more than twice as many pixels as 720x576. It will require about twice the bitrate with the same codec. Of course, you're comparing 1280x720 encoded with h.264 to 720x576 encoded with MPEG 2. Since h.264 is roughly twice as efficient as MEPG 2 you will need about the same bitrate as DVD. In the ballpark of 4000 to 8000 kbps.

[Emanef]

Do you know why converting to 720x576 gives me a resolution of 1024x576? Even if I set the resolution (using RipBot) to that res, the resulting mkv or mp4 reports in MediaInfo as being 1024x576.

I have tried capturing standard def recodings at 576 on the Sky HD, but for some reason, as soon as I turn the telly off, the aspect ratio on the Arcsoft capture module changes and it goes all squashed! Very strange!

[jagabo]

You are specifying square pixel encoding. So a 16:9 source turns out 1024x576 (576 * 16 / 9 = 1024). Specify PAL 16:9 PAR instead.

[Emanef]

Ah, ok, I'm with you. Presumably the same file done at the same bit rate would be a little smaller if I specify PAR. I've been using Staxrip and Ripbot for converting, so I'll see if I can find out how to specify that and do a couple of tests.

[Emanef]

Hmmm, interesting. I've just tried a 5 min cutting from Sunshine at both 720x576 and 1024x576 in Staxrip. Exactly the same size and exactly the same bit rate.

So which am I best to use, for playing back on a normal HD TV? Does it actually make any difference?

I think what I may be doing is converting my favourites to higher quality, and resizing others I want to keep but don't need the quality from 720 to 576. I think I may prefer that over capturing at 576i, as they'll be 576p anyway.

[jagabo]

file size = bitrate * running time

This is independent of the frame size. But a larger frame will give less quality at the same bitrate. Especially at lower bitrates

For best quality encode at the same frame size as your source and use PAR/DAR flags to tell the player the final shape (16:9 or 4:3) of the image.

[Emanef]

OK, thanks. So a 720 with the same bit rate will be the same size as a 576 of the same bit rate, but because of the larger resolution the quality will be less. I was thinking that two identical files of differing frame sizes with the same bit rate would have the same quality, but the larger frame file be larger. I've got it the wrong way round then!

I've got the day off work so am trying a few tests for comparison. I've done a few at 720 and 576 (720*576) but I it's too bright to be able to see the telly clear enough to do a eye good comparison! Makes a change! I'll try a little later!

[jagabo]

It's like miles per gallon. No matter how big the vehicle, if it gets 20 miles per gallon, it will go 20 miles on one gallon of gas.

[deadsimple]

Hi Guys
I'm having a major sync problem, when playing the recorded Sky HD content via Hauppauge HD PVR. this is becoming more apparent when I burn a AVCHD DVD. I'm using Vista 32 and Arcsoft TME. Sorry if this has been discussed earlier but any auggestions will be grately appreciated.
Deadsimple

[ChrissyBoy]

It's like miles per gallon. No matter how big the vehicle, if it gets 20 miles per gallon, it will go 20 miles on one gallon of gas.

One of the best analogies I’ve seen!!! - Nice.